Case Study: Ultra Precision SAW Scales Enable Continuous Mode Bioreactors for Pharmaceuticals


One of our largest customers manufactures bioreactors for their pharmaceutical clients. A bioreactor is a device that is designed to grow organisms under controlled conditions. They can include bacteria, animal cells, yeast, algae, or a host of others. These organisms are used in an ever widening range of pharmaceuticals, vaccines, antibodies, and other industrial processes.

There are three main types of bioreactors.

  • Batch Process
  • Fed-batch Process
  • Continuous Process

Batch Mode

This is the simplest, but the least economical process in production. All the nutrients are provided at the beginning of the cultivation. The bioprocess continues until all of the nutrients are consumed. The limiting factor is generally the carbon source or the oxygen transfer. Increasing the stirring speed, gas flow or pressure can be helpful. The result is a mix of nutrients, reagents, cell debris and toxins, along with the desired end product.

Fed-batch Mode

To extend the culture’s productive duration, a Fed-batch process continuously supplies nutrients. The total yield can be significantly increased, but the major disadvantages remain.

Continuous Mode

A major provider to the bioreactor industry needed to offer a Continuous Process system to their customers. Once the process reaches equilibrium, the amount of fresh medium added has to match the amount that is removed for cell harvesting. Filters are used for the perfusion process.


In the Continuous Mode Bioreactor, the challenge was to accurately weigh the small amounts that were being removed from the process. To measure these miniscule amounts of weight, the customer needed a scale that would have a large enough weight capacity to accept the bioreactor, but have high enough accuracy to measure the very small amounts removed.

They also needed the scale to output weight data to their perfusion system so that the system could adjust the reactor based on weight readings.

To summarize the issue, they needed a scale that:

  • Was extremely accurate.
  • Had a very high capacity
  • Could measure very low weight increments (ultra-high resolution)
  • Was able to output weight data into their perfusion system.


To counter the challenge presented by this customer, we outfitted the customer’s perfusion bioreactors with the Model SAW-KL. This scale is part of Arlyn’s Ultra Precision Scale product line. The SAW-KL and its model variants use the same technology as Arlyn’s Ultra Precision Scales, but they utilize larger load cells to accommodate even bigger capacities. Using an all digital Surface Acoustic Wave (SAW) transducer, these scales provide more than 10 times better accuracy than any other scale in its price range. As a bonus, they are also more rugged than regular scales, and can be used in a wide variety of industrial applications.

The SAW-KL Large Ultra Precision Scale met the customer’s requirements based on the following specifications:

  1. The SAW-KL has a capacity of 225kg, allowing it to accept a reasonably sized bioreactor.
  2. It is able to measure ultra low weight increments of just 2g. That is a factor of 1:100,000 of full scale. This resolution is also 20x higher than most strain gage weighing scales existing today.
  3. The SAW-KL could also be equipped with RS-232 Digital output. This allowed the weight data to be communicated to the bioreactor controller, allowing the proper amounts of fresh medium to be added when required.


With the proposal of this solution, we were able to support one of the largest manufacturers of pharmaceutical bioreactors in the industry. The Ultra Precision SAW scales by Arlyn Scales provide a unique solution to many challenging needs in the Pharmaceutical Industry, due to the fact that it is able to support very high capacities while providing extremely precise, ultra accurate and highly granular weight measurements.